<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <input type="button" value="按钮" id="btn">
  <script src="common.js"></script>
  <script>
    var btn = my$('btn');
    function btnClick() {
      alert('hello');
      // 移除事件
      removeEventListener(btn, 'click', btnClick);
    }
    addEventListener(btn, 'click', btnClick);
  </script>
</body>
</html>
